The authors describe the pharmacological effects of theophylline and elucidate its mechanisms of action according to latest hypothesis. The narrow therapeutic range of the drug and the existence of factors capable of modifying its distribution and clearance in the elderly, are taken into consideration, as well. The behaviour of theophylline concentrations in two groups of elderly subjects affected by chronic bronchitis, treated respectively with intravenous aminophylline and anhydrous theophylline administered orally are assessed. Usefulness of associating the two routes of administration is underlined. In fact, the delay in the achievement of the therapeutic range observed after oral intake can be made up for by the initial peak induced by intravenous injection. Our observations in the elderly are consistent with the necessity of therapeutic monitoring. In addition, a careful dosage of the drug can avoid the occurrence of untoward effects.